🐛 fix(test): correct error message assertion case

- change expected error message from 'Not found' to 'not found' to match actual response case

packages/shared-test-util/src/integration-test-utils.ts

@@ -170,7 +170,7 @@ export class ApiResponseAssertions {
    */
   static expectNotFound(response: { status: number; data: any }): void {
     IntegrationTestAssertions.expectStatus(response, 404);
-    IntegrationTestAssertions.expectErrorResponse(response, 'Not found');
+    IntegrationTestAssertions.expectErrorResponse(response, 'not found');
   }
 
   /**